1. Field of Invention
This invention relates to a method of selectively removing lipoproteins from blood plasma or serum.
2. Description of the Prior Art
The fractional separation of the numerous species of proteins occurring in plasma or serum has been of considerable interest to investigators for nearly a century. Advances have been made with the result that some of the protein species are now harvested industrially with a high degree of purity e.g. fibrinogen, .gamma.-globulins and albumin. However any attempt at the isolation of one of the plasma or serum proteins is hindered by a variety of technical problems, a common one being the presence of sizeable amounts of lipoproteins. These are not easily removed selectively, least of all on a large scale.
Ion exchangers work on charge-charge interaction between the exchanger and the substance sought to be bound to the exchanger and thus isolated from the fluid. It is to be expected that where there is a plurality of species of similar charge a particular species would not be selectively removed by an ion exchanger. We have now quite unexpectedly found that cationic ion exchangers whose ion exchange capacity is provided by sulphate groups bind lipoproteins selectively in the presence of all other serum proteins and ions when they are equilibriated with solutions containing divalent cations, such as magnesium, calcium and manganese and the same divalent cation is added to the serum. The concentration of the cation required in the serum depends on the character of the matrix sulphated, the extent of the sulphation, the cation and the pH of the serum. Preferably the concentration is in the range 0.05 to 1.0 M and a pH between 6 and 8. Suitable parameters are more particularly set out in the following examples.
It has been observed that elevated plasma lipoprotein concentration is frequently a secondary phenomenon associated with primary diseases such as diabetes mellitus, hypothyroidism, heavy proteinuria and obstructive jaundice. In addition, over the past quarter century data have been gathered which tend to suggest a direct correlation between plasma lipoprotein concentration and the incidence of clinical coronary artery disease.
Lipoproteins in blood plasma comprise three primary fractions, the very low density (VLDL) fraction, the low density (LDL) fraction and the high density (HDL) fraction. A high concentration of the second of these has been observed in patients who have suffered coronary artery disease. A fuller review of this background to the invention may be found in "Blood Lipids and Lipoproteins Quantitation, Composition and Metabolism." Edited, Gary J. Nelson, John Wiley & Son Inc. U.S.A., 1972. It will be appreciated that a simple method of testing for such an abnormality as a matter of routine in an annual medical examination is highly desirable. A patient thus warned could take corrective steps such as changes in diet or commence taking medication to reduce the unwanted concentration to lessen the possibility that he might be subject to coronary disease. Methods which have been used up to now to determine the relative concentration of the fractions of the lipoproteins in blood have involved tedious precipitation and centrifugings and the quantitative resolution has been something less than satisfactory (Cf. Journal of Lipid Research, Vol 11, 1970 pp 583 to 595.
It is an object of this invention to go some way towards alleviating these disadvantages or at least to provide the public with a useful choice.